1. Field of the Invention
The present invention relates to devices and methods for reinforcing drill string components used in drilling operations. More particularly, it relates to a portable apparatus and method for welding a hard metal band onto a portion of a drill pipe or drill collar section.
2. The Prior Art
In the production of wells for the recovery of oil, gas and other natural resources, it is common to utilize rotational drill strings that vary anywhere from several hundred feet to several miles in length. A drill string consists of a plurality of discrete sections that are rigidly connected together as the drill string is advanced into the well. Each discrete section is typically comprised of one of two general section types: drill pipes or drill collars.
A drill pipe consists of an elongated tubular pipe approximately 32 feet in length, having an outer diameter ranging from approximately three and one-half inches to approximatley six and three-quarter inches, and weighing anywhere from 280 to 14,000 lbs. Welded to each end of the elongated tubular pipe are tool joints, the means by which the drill pipe sections are connected together in forming the drill string. Each section of drill pipe has one male tool joint, referred to as the pin end, and one female tool joint referred to as the box end. The pin and box ends are provided with complimentary threaded portions so as to facilitate the rigid joinder of two or more drill pipe sections in forming the drill string.
Drill collars differ from drill pipe in that the threaded male and female tool joints are machined directly into the elongated tubular pipe. Otherwise, drill pipe and drill collars are similar and generally suffer from the same inherent weaknesses. For ease of explanation, therefore, only drill collars will be discussed herein with the understanding that the same considerations generally apply to drill pipe as well, unless otherwise indicated.
In the course of a normal drilling operation, the drill string is subject to substantial frictional wear and significant stress. As a general rule, tool joints are the part of the drill string most susceptible to failure, and the useful lifetime of most drill collars is, therefore, directly dependent on the durability and structural integrity of the tool joints.
In an effort to prolong the useful lifetime of the drill collars, it is common to apply a band of hardened metal (i.e., steel hardened through the use of a tungsten carbide filler) to the outer surface of the drill collar in close proximity to the tool joints. Such hard metal bands (herein referred to as "hardbands") are typically applied to the drill collars according to conventional metal-inert-gas (herein referred to as "MIG") or tungsten-inert-gas (herein referred to as "TIG") welding processes. The use of hardbands has proven to be extremely effective both in retarding the rate of frictional wear at the tool joints and in significantly improving the tool joint's structural strength.
The most effective hardbanding technique presently in use is referred to as "raised face" hardbanding in which the hardbands are welded directly onto the surface of the drill collars so as to present a larger overall diameter than the outer diameter of the drill collar itself. Frictional forces are thus focused at the thicker hardbanded regions during drilling operations such that the hardbands absorb most of the wear rather than the tool joints or the drill collar itself. According to this method, it is possible to extend the lifetime of a drill collar essentially indefinitely by periodically replacing the hardbands as they wear down.
In the past, hardbands were only applied to drill collars at permanent hardbanding facilities, most of which were located at the places where the drill collars were manufactured. This required that the collars be transported large distances and be serviced on a first come first serve basis each time the bands were to be replaced. It will be appreciated that the turn-around time involved in such a procedure required the drilling operator to maintain a substantial inventory of hardbanded drill collars so that the periodic maintenance or replacement of worn drill collars would not necessitate a lengthy and expensive shutdown.
More recently it has become popular to utilize portable hardbanding devices capable of being transported to the drilling location for on-site hardbanding in order to greatly reduce the prohibitive cost of this operation, as well as to essentially eliminate the extensive loss of drill collar use, during the extended period required for sending drill collars to a permanent hardbanding facility.
Although portable hardbanders provide definite advantages over permanent hardbanding facilities, they pose a number of significant problems in design. For example, the size and weight of the equipment which makes up the hardbander must be such that the device can be transported with the least amount of difficulty and expense. However, the safety and efficiency of the system are essentially proportional to the amount of equipment available for materials handling and power generation, respectively. Thus it is desirable to minimize the size and weight of the system to provide for ease in transportation, while still providing the amount and types of equipment necessary for safe and efficient operation. Thus, the optimum design would comprise a portable hardbander that is safe and efficient, and that maximizes the economic benefit to the consumer.
The portable hardbanders found in the prior art represent unsuccessful attempts at meeting these requirements. The prior art devices are generally inadequate in the following areas: (1) the devices are relatively slow in operation, resulting in a higher per unit hardbanding cost; (2) the devices do not provide adequate controls for monitoring the weld content and quality; and (3) the devices are relatively unsafe, resulting in a high incidence of operator injury.
The speed of a hardbander is directly related to the power capability of the system. In a welding process of the type used in hardbanding, electrical current of a very high magnitude is required. The hardbanders found in the prior art generally rely on standard direct current (DC) generators for weld power. Such generators typically produce, at most, 350-450 amps of current. If, however, an alternator were used, alternating current (AC) of 600-700 amps could be produced. Current of this magnitude would significantly increase the speed of the hardbanding process. Moreover, AC equipment provides additional advantages in size and weight since it is inherently lighter and less bulky than DC equipment.
The prior art devices are generally provided with rather crude controls for controlling such things as the welding wire feed rate and the hard metal feed rate. Typically, adjustments of these feed rates are made according to visual inspection and operator estimates. Thus, with these devices, continuous visual observation of the weld by the operator is essential for maintaining the proper feed rates. Moreover, prior art devices do not provide any means beyond operator estimate for making an accurate determination of the weld content. If the weld content is not carefully controlled, the result may be substandard, brittle hardbands which readily crack and break. The prior art devices are, therefore, very susceptible to operator error and do not provide the necessary equipment for adequately controlling hardband quality.
Finally, a serious problem with prior art portable hardbanders is that their operation may be somewhat hazardous to the operator. Most of the prior art portable hardbanders utilize a standard three jaw lathe chuck to rotate the drill collars adjacent to the welding assembly. In most cases, the lathe chuck must be fastened around the drill collars at a point only 2 to 3 inches from the end of the drill collar. As a result of extensive use of the lathe chuck system, it has been found that vibrations and/or slight movement of the collar relative to the lathe chuck can cause a drill collar to work itself free of the lathe chuck and fall to the ground. It will be readily appreciated that an operator working in close proximity to such a device is not in jeopardy of having one of these massive drill collars fall on him, causing a severe injury.
Thus, what is needed in the art is a portable hardbander that is readily and inexpensively transportable, that is safe in operation, that has increased power capability and that provides means for accurately monitoring and controlling the content and quality of the hardbands. Such a device is described and claimed herein.